The conventional impact-absorbing means may include metal springs, friction-type attenuators, hydraulic attenuators, and molded rubber parts. In some cases, these means may be used in any combination. The metal springs, although they have excellent attenuation performance, exhibit almost no impact energy absorption capacity. The friction-type attenuators and hydraulic attenuators are usually complex in structure, and they have a problem that their spring constants have extremely great dependence upon the rate of deformation and these attenuators, therefore, have no restoration.
The molded rubber parts are characterized by their good restoration, but on the other hand, they have a drawback that the material should be used in larger amounts for securing satisfactory impact absorption because of having a low elastic modulus and the member, therefore, has an increased weight and becomes large in size.
As the impact-absorbing means with shaped resin parts, the present inventors have proposed an impact absorber comprising a shaped resin part with cushioning properties, which is provided with two or more arched, domed, or other shaped compression-deformable portions on a perforated or unperforated flat board. The impact absorber, however, has problems that it exhibits small impact energy absorption and it is difficult of application in the case where it should be disposed in a limited space.
As the impact absorber with shaped resin parts, there is disclosed a technique for the production of shaped resin parts, characterized in that hollow shaped parts made of a thermoplastic elastomer are given permanent strain by compression in the axial direction (see Japanese Patent Publication No. 61-12779). The shaped resin parts obtained by this technique, although they have excellent attenuation performance, have a problem that they only exhibit a poor collision energy absorption capacity.